Add track publication, album types, optional track pictures and batch upload URLs

Tracks
- Track.IsPublished (migration marks existing tracks as published). New
  tracks are created unpublished.
- PUT /tracks/{id}/published and PUT /tracks/published change the flag;
  publishing requires completed audio processing (the batch endpoint
  reports skipped tracks).
- An unpublished track is only visible to its owner. A WherePublished /
  VisibleTo filter is applied to search, genres, listening history, last
  listened, likes, mixes, album and playlist contents and counts, recently
  listened albums, public user tracks, track details and stream tickets.
- isPublished is part of the track responses, GET /tracks/users/{userId}
  accepts a published filter and status-counts reports published and
  unpublished totals.
- CreateTrackRequest.pictureIntentId is optional: without it the track
  uses the album cover or the preset picture and no picture processing
  runs. CreateTrackResourcesEvent carries nullable picture fields, so
  queues must be drained before deploying.
- POST /tracks/upload-urls accepts an audios list and one optional picture
  shared by all of them, and returns an intent per file. The upload intent
  limits are raised so a batch fits.

Albums
- AlbumType (Album, EP, Single) on create, update and responses.
- CreateAlbumRequest.trackIds creates the album and links the tracks in a
  single save.

backend/Hosts/Musify.Api/DataTransferObjects/Tracks/RequestTrackUploadUrlsRequest.cs

@@ -1,10 +1,16 @@
 namespace Musify.Api.DataTransferObjects.Tracks
 {
+    public record AudioUploadRequest(
+        string FileType,
+        string ContentType,
+        long? ExpectedSizeBytes = null);
+
     public record RequestTrackUploadUrlsRequest(
-        string PictureFileType,
-        string PictureContentType,
-        string AudioFileType,
-        string AudioContentType,
+        string? PictureFileType = null,
+        string? PictureContentType = null,
+        string? AudioFileType = null,
+        string? AudioContentType = null,
         long? ExpectedPictureSizeBytes = null,
-        long? ExpectedAudioSizeBytes = null);
+        long? ExpectedAudioSizeBytes = null,
+        IReadOnlyList<AudioUploadRequest>? Audios = null);
 }